An attack team is a group of soldiers sent in as reinforcements when Alert Mode is triggered. They often have heavier and more protective armor, greater firepower (shotguns and grenades) and often better abilities than their guard team counterparts.
Attack teams are a punishment to the player for being caught and hence it is generally best to just avoid triggering Alert Mode entirely. However, in some areas, because of a lack of manpower to deploy into the area, an attack team will not be deployed even if an Alert Mode is triggered. They can also be deployed if either suspicious activity is reported or if the guard team is unable to give a status report on time.
In Metal Gear Solid 2: Sons of Liberty, they often carry full length riot or ballistic shields, making it necessary to aim for head or foot-shots. It is possible to shatter these shields with repeated shots, though it requires more ammo than it's generally worth and a headshot is recommended to neutralize them. Other members of an attack team are equipped with body armor and either a shotgun or an Assault Rifle (AN-94) or Carbine (AKS-74u). In certain areas later in the game, Hi-Tech Soldiers - wearing suits that resemble bombsuits and make them much more resistant to damage, even to the head - can be part, or make up all, of the attack team. These Troopers will all be armed with M4A1s, with some of them eqiuped with an M203 Grenade Launcher. Unlike regular guards, attack teams have no dog tags or any Items to take.
In Metal Gear Solid: Portable Ops, attack teams may arrive with the same weapons as the guard team, a ballistic shield or a different weapon with greater firepower than the guard team with little or no extra equipment than the guard teams as they rely on soldiers stationed in other areas since the game is set on an isolated peninsula.
They are difficult to escape from as they will clear rooms they think you are hiding in, search for you in lockers and shoot at boxes that look out of place or unusual, and especially arrive in pairs or greater numbers (on some occasions, just one will arrive).
But should they be encountered during the course of the gameplay, they should be dealt with as soon as possible and a spot must be found to hide in until the everything is normal again. Alternatively, hiding in somewhere they can't look (the middle of a long air duct, for example) or leave the area and hide elsewhere is recommended.
It is important to evade a second wave or consecutive waves of enemies if the first wave of enemies are neutralized.
In Metal Gear Solid 3: Snake Eater, simply incapacitating the entire attack team is generally enough to get away, if it comes to that, since only one wave comes (alternatively, in some areas such as the Shagohod hangar, it is possible to set traps for the only ways the attack team can enter, then intentionally sound an alarm, defeating the attack team and leaving you free to go about your business). Often attack teams are more difficult to hold up and reluctant to surrender as they will attack at the first available opportunity (as they have been trained to attack from behind). In addition, the Single Action Army is useful for its ability to ricochet bullets and hit the soldier from behind.
In Portable Ops, attack teams are more brave and will not give up items when a weapon is pointed at their head except for an RPG-7 which will frighten them.